Air preheater control system



Oct. 9, 1951 R. RASMUSSEN 9 AIR- PREHEATER CONTROL SYSTEM Filed July 19, 1948 FLOW ng TRANSMITTER E TEMPERATURE 4| TOTALIZER E- I2 4 46 GAS oUTLET AIR 43 40 53 INLET Z E i Z DAMPER, I8 MOTOR 29 60 56 55 K 6| W 7/77 52 &i 3| 50 A53 6 I 6 fi 'T' "3. (r W Y r "I 1 I Z 1 25 swam/tow ROBERT RASMU SSEN ATTORNEYS Patented Oct. 9, 1951 '1 QFFICE- AIR PREHEATER CONTROL SYSTEM Robert Rasmussen, Detroit, Mich., assignor, by

mesne assignments, toJThe Air Preheater Corporation, New York,,N. Y., a corporation of New York Application July 19, 1948, Serial No. 39,538

The present invention relates to an air preheater control system.

It is an object of the present invention to provide an air preheater control system having interdependent means for eflecting a by-pass of air around or a recirculation of air through an air I heater.

1 Claim. (Cl. 257-6) It is a further object of the present invention to provide an air preheater system comprising a heater, a cold air duct for conducting coldair to the heater, a preheated air duct leading from the heater, a recirculation duct connecting the preheated air duct 'to'the cold air duct, a bypass duct connecting the cold air duct to the preheated air duct, a blower in the cold air duct intermediate the connections thereto of the recirculation duct and the by-pass duct, an automatically controlled damper in therecirculation duct adapted to close automatically as said blower attains full load conditions, a recirculation damper in the recirculation duct, a by-pass damper in the by-pass duct, a single control means for both of said last mentioned dampers adapted upon actuation to efiect sequential opening of said dampers, the arrangement being such that the recirculation damper opens fully-before thebypass damper commences to open.

It is a feature of the present invention to provide inan air preheating system, independent dampers for controlling recirculation of air through the heater or by-pass of air around the heater including actuating members for said dampers, slotted link means for actuating said levers, and a control member for moving said link means, the slots therein being arranged such 7 that upon movement of said control member from one limiting position to the other, it will first efiect full opening movement of the recirculation damper and thereafter effect opening movement of the by-pass damper.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, wherein:

The single figure is a diagrammatic view illustrating the air preheater control system.

Referring now to the drawing, there is illustrated a heat exchanger at H) which may be of any desired type adapted to eifect heat transfer 2 from hot flue gases to combustion air. As illustrated in the figure, a duct I I for hot gases leads to the heat exchanger t and a second conduit l2 connects to the uptake. A cold air duct is indicated at l5 which has an inlet as shown at It inducts atmospheric air from outside the building in which the preheater) is located. As shown the upper end of this duct is opened to receive ambient air from the boiler room or other space in which the preheater H] is mounted. Suitable dampers are provided as shown so that either source of relatively cold air may be shut off, wholly or partially. The cold air duct I5 is provided with a forced draft blower or fan as indicated diagrammatically at I8, the outlet from this fan forming a continuation 20 of the cold air duct through which air is forced to the heat exchange member |0. The air passes through the heat exchanger I!) in heat transfer relation to the hot flue gases therein and a preheated air duct 25 is provided leading from the air heater through which the preheated air flows to the furnace.

Interconnecting the preheated air duct 25 and the cold air duct I5 is a recirculation air duct which is provided with an automatic operable damper 3|. Suitable means are provided for controlling speed of the blower l8 in accordance with the demand of the furnace and means are provided responsive to the load on the blower for causing the damper 3| to start to close as the blower approaches full load conditions. These may include a flow meter 2| for measuring the rate of air flow through the inlet duct 20 and acting through the impulse transmitter 22 to actuate a damper motor 23 and operate the damper 3| through an arm 24 in response to the load onthe fan I8. When the blower is operating at full capacity, the damper 3| will be closed.

A by-pass duct is provided which connects the cold air extension 20 to the preheated air duct 25. It will be observed that the blower H3 is located between the connections of the recirculation air duct 30 and the by-pass air duct 35 to the cold air duct system I5, 20. As a result of these connections the flow of air through the various ducts is as indicated by the arrows.

A problem in air preheaters of this type is the maintenance of suitable temperature for the exhaust gases, inasmuch as these gases are highly corrosive if condensation is permitted in the heat exchanger. In accordance with the present invention dampers are provided in the recirculation ducts and in the by-pass duct for controlling circulation of air through the heater so as to prevent condensation of flue gases therein. Means are provided for controlling these last mentioned dampers in a particular sequence and if desired this means may be automatically operated or it may be manually actuated. If automatic it will be controlled by means responsive to the temperature of cold air entering the heater and the cooled gases as: they leave the air heater. If the control means is manual, a suitable remote control operating means will normally be provided adjacent the control panel so that changes in the air system' may be issued in accordance with the indicated temperatures shown on the panel.

'A by-pass damper 4B is provided at theinlet end of the by-pass duct 35. The damper 4E! is mounted for swinging movement about a pivot. indicated at 4| and an operating lever 42 is secured thereto. Suitable means are provided for biasing the by-pass damper 40 toward closed position and in the illustrated embodiment this means takes the form of a counterweight 43. The operating lever d2 extends beyond the pivot 41 and has suitable means such as a pin indicated at 44 which engages in a slot 45 formed in an operating link 45'. Located in the recirculation duct 30 is a normally opened damper 5% which is mounted for swinging movement about a pivot 5! and which has secured thereto an operating lever 52. The lever 52 is provided with means normally urging the damper 58 toward open position. and this means is illustrated herein as comprising a counterweight 53. The operating lever 52 is provided with a pin or the like as indicated at 54 which engages in a slot 55 formed in an operating link 56.

While the links 46 and 55 are herein shown as in the form of a single elongated member it will be appreciated that if desired they could be independent members.

Means are provided for effecting simultaneous actuation of the links 46 and 56 and this means as illustrated takes the form of an operating lever 60 pivoted as indicated at 6! and having a counterweight 62 thereon. The lever 6t may be operated directly or it may be operated by suitable control means such for example as a double acting cable or the like.

Due to the provision of the counterweight 43 the by-pass damper is normally closed but is movable from the closed full line position shown to the doted line position indicated in the figure. In like manner due to the provision of the counterweight 53 the recirculation damper 59 is normally open but is movable by the link 56 from the normally open position indicated in dotted lines in the figure to the closed position shown in. full lines. The automatic apparatus may comprise thermostats 25 and 2? in the gas outlet and air inlet ducts i2, 20 respectively. The indications of thermostats 26, 2'! are averaged in a totalizer designated as a whole by the numeral 28 which may be a pneumatic control apparatus such as described in Cooper Patent 2,320,911, issued June 1, 1943. As more fully described in said patent, variations in the average of the air inlet and gas outlet temperatures from a predetermined standard value are reflected in the operation of an air motor 29 which is operatively connected to the damper lever ti] so as to actuate the dampers 40 and 5E] accordingly.

With the parts shown in the relative position illustrated in the figure, both the by-pass damper 40 and the recirculation damper 53 are in closed position. The recirculation damper 59 is retained in closed position by the link 55. The by-pass damper 4B is closed since the pin 44 is at the lower end of the slot 45. If now the average temperature of cold air passing to the heater and the temperature of the cooled gases leaving the heat exchanger reaches a predetermined mimimum, the operating lever will be rotated in a counterclockwise direction either by direct manipulation of the lever or by suitable remote control means which may be either manual or automatic in operation. Initial counterclockwise movement of the lever 60 causes the links 46 and 56 to move downwardly. The first downward movement of the link 56 permits the recirculation damper 50 to commence to open. The first downward movement of the link 46 has no effect on the by-pass damper 40, since this movement is merely accompanied by a movement of the pin 44 relatively upwardly in the slot 45. The slots 45 and 55 are so designed that when downward movement of the link 56 has permitted the recirculation damper 50 to move to full open position, further downward movement of the links will cause the upper end of the slot 45 to move the operating lever 42 so as to commence to open the by-pass damper 40.

As will be apparent initial opening movement of the recirculation damper 59 will permit some of the preheated air in the preheated air duct 25 to return to the cold air duct l 5 and thence to recirculate through the air heater 10. This will reduce the cooling efiect of the cold air on the hot gases and may be suihcient to prevent condensation of flue gases. However, when this recirculation of preheated air has reached a maximum eflicient amount, it may prove to be insufficient to prevent condensation from the flue gases. Accordingly, as further correction is required, further movement of the lever 69 opens the by-pass damper 48 thus reducing the amount of cool and recirculated preheated air which passes through the heat exchanger.

According to the foregoing, control of the position of the'dampers 40. and 50 is dependent entirely upon temperature conditions in the air heater and specifically upon the temperature of the cold air entering the heater and the tempera ture of the. cooled gases as they leave the heater. It is desirable to maintain a minimum average temperature of cold air in and cooled gases out so long of course as these temperatures do not result in condensation of corrosive products from the flue gases. In accordance with the present invention the operator need at no time be concerned with the actual position of the dampers 40 and 59 nor need he be concerned if the forced draft blower is operating nearcapacity since the automatically operated damper ill will shut off recirculation of the preheated air as required.

This control system is designed to maintain a minimum average of temperature of air to the air heater and gas leaving the air heater. This minimum temperature is a safe margin above the dew point of the flue gases. 7 When during thebperation the forced draft blower approaches full 7 load, the automatically operated damper 3! starts in the art to practice the invention, the scope of which is indicated by the appended claim.

What I claim as my invention is:

In an air preheater system including an air heater, means for by-passing cold air around said heater including a by-pass damper, means for recirculating preheated air through said heater including a recirculation damper, means normally urging said recirculation damper toward open position, means normally urging said by-pass damper toward closed position, levers for moving said dampers, slotted link means cooperating with said levers, means for moving said link means between limiting positions, said link means in one limiting position holding said recirculation damper closed and permitting said bypass damper to close, the slots on said link means being disposed to permit complete opening of said recirculation damper and thereafter to efiect opening of said by-pass damper upon movement from said one limiting position.

ROBERT RASMUSSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,343,330 Miles June 15, 1920 2,320,911 Cooper June 1, 1943 2,363,870 Karlsson et al. Nov. 28, 1944 2,499,358 Cooper et al. Mar. '7, 1950 

